1. Field of the Invention
The present invention relates in general to optical devices and in particular to an optical derotator incorporating multiple dove prisms configured as wave transmitting prisms.
2. Related Art
Optical systems, such as periscopic scanning devices, are used to view objects with a detector. However, optical systems without derotation devices introduce image rotation at a focus point of the optical system. In an ordinary periscope, the detector (eye) rotates to accommodate this image rotation. While rotating electronic detectors have been used, it is desirable for the detector to be fixed. Consequently, the detector is not presented with a true image orientation of the object being viewed.
One way to prevent rotation is to utilize a system of plural reflecting surfaces to modify an optical path of light rays of the optical system. Typically, at least three reflecting surfaces are introduced into the optical path of light rays to provide image derotation. However, the usual optical system with plural reflecting surfaces occupies too much space. Also, reflective systems may have uneven image illumination due to partial blockage.
Dove prisms are commonly used for major image derotation in refractive optical systems that require mechanical rotation of the optical system to provide 360.degree. azimuthal coverage of the image, such as scanning devices. Those dove prisms are relatively expensive and large and bulky.
Therefore, what is needed is an optical assembly for efficiently and effectively causing image rotation that may also be used to derotate images which are rotated by other parts of an optical system. What is further needed is an optical derotation assembly that is relatively small and lightweight.
Whatever the merits of the above mentioned systems and methods, they do not achieve the benefits of the present invention.